well you could have ovulated late.. which will make your period late, or a false negative pregnancy test. If you go and get a blood test from your doctor .. i would ask for quantitative (where they tell you the number of your hormones and not just if positive or negative.... ) Sometimes you could be pregnant still wit hthe blood test and if you are not above a certain hormone level.. it will say negative. I had this happen in the past.
As for the ovulation,.. not everyone ovulates on cd14... and it can very from month to month also.,.
Are you keeping track of your cycles, like temping, OPK's., that sort of thing?